The invention relates to a piezoelectric actuator, and more particularly to a piezoelectric actuator with a displacement enlarging feature.
In the prior art, various type piezoelectric actuators have known, one of which will be described with reference to FIG. 1. The conventional piezoelectric actuator has a mounting substrate 21, lever arms 23 being mechanically connected through hinges 22 on opposite sides in one direction of the mounting substrate 21, a piezoelectric device 24 being provided in a rear side of the mounting substrate 21 and being mechanically connected to rear ends of the lever arms 23 and a beam 25 being provided in a front side of the mounting substrate 21 and being mechanically connected to front ends of the lever arms 23. The beam 25 has a larger length than a distance between front ends of the lever arms 23 so that the beam 25 always has a small curvature wherein a center portion of the beam 25 lies at a higher level than that of the opposite end portions of the beams 25.
When the piezoelectric device 24 is applied with a voltage, then the lever arms 23 move around the hinges 22 as supporting points so as to reduce the distance between the front ends of the lever arms 23 thereby the curvature of the beam 25 becomes large. As a result, an amount of the displacement of the center portion of the beam 25 becomes large.
The above piezoelectric actuator has a disadvantage as follows. If ,the piezoelectric device in the actuator comes into failure, an exchange of the piezoelectric device is required. However, the piezoelectric device is securely fixed to the lever arms by a thermosstring adhesive. For that reason, if any failure appears in the piezoelectric device, then it is required to exchange the actuator and all. Further, if it is required to change a performance of the piezoelectric device only, then the actuator and all are exchanged.
The above structure of the piezoelectric actuator also has a disadvantage as follows. The piezoelectric device has a poor resistivity to the tensile load, but a sufficient resistivity to the compression load. For that reason, it is preferable to always apply a preload or a small compression load to the piezoelectric device. Notwithstanding, the above structure of the conventional piezoelectric actuator has no feature to apply any compression load to the piezoelectric device.
Another type of the conventional piezoelectric actuator is disclosed in the Japanese patent application No. 3-89873, a structure of which is illustrated in FIG. 2. The piezoelectric actuator has a piezoelectric device 31, a movable member 32 securely fixed to the piezoelectric device 31 to transmit a displacement of the piezoelectric device 31 into an exterior, an elastic member 33 for pressing up the movable member 32 to apply a preload or a compression load to the piezoelectric device 31 and a case 39 for accommodating the piezoelectric device 31, the movable member 32 and the elastic member 33 and further a guide 35 fixed to the case 39 for providing a guide for motion of the movable member 32.
The above piezoelectric actuator has a disadvantage as follows. If the piezoelectric device in the actuator comes into failure, an exchange of the piezoelectric device is required. However, the piezoelectric device is securely fixed to the case 39 of the actuator. If any failure appears in the piezoelectric device, then it is required to exchange the actuator and all. Further, if it is required to change a performance of the piezoelectric device only, then the actuator and all are exchanged.
Further, the above actuator has no displacement enlarging feature. For that reason, if a large displacement of the movable member, then it is required to design the piezoelectric device to have a large length in an expanding direction thereof.
Still another type of the conventional piezoelectric actuator is disclosed in the Japanese Patent Application No. 3-218274, whose structure is illustrated in FIG. 3. The piezoelectric actuator has a substrate 41, a cylindrically shaped piezoelectric device 42 being provided over the substrate 41 through an insulator so that the piezoelectric device 42 is isolated from the substrate 41. A movable member 43 is securely fixed on the piezoelectric device 42 to transmit a displacement of the piezoelectric device 42 to an exterior. A spring member 44 is provided between top portion of the frames united with the substrate and %he movable member 43 so that the spring member 44 presses down the movable member 43 to apply a reload or a compression load to the cylindrically shaped piezoelectric device 42.
The above piezoelectric actuator has a disadvantage are follows. If the piezoelectric device in the actuator comes into failure, an exchange of the piezoelectric device is required. However, the piezoelectric device is securely fixed to the substrate of the actuator. If any failure appears in the piezoelectric device, then it is required to exchange the actuator and all. Further, if it is required to change a performance of the piezoelectric device only, then the actuator and all are exchanged.
Further, the above actuator has no displacement enlarging feature. For that reason, if a large displacement of the movable member, then it is required to design the piezoelectric device to have a large length in an expanding direction thereof.
The cylindrical shape of the piezoelectric device 42 has a poor resistivity to a load in the radius direction.